Heroin user who killed dog walker jailed for at least five years

A young motorist who struck and killed a man walking his dog while driving erratically under the influence of heroin east of Melbourne has been jailed for at least five years.

Dillon Buckley, 27, was found to have caused the death of 58-year-old Guy Williams, seriously injured his partner Mardi Trease, 68, and injured their dog when he hit them from behind at Wandin East on December 9 last year.

He had taken heroin 15 minutes earlier.

Guy Williams was struck from behind the horror collision. (9news)Dillon Buckley, 27, told a witness he "didn't care" that he had just struck the couple. (9NEWS)

Witnesses variously observed Buckley driving erratically, cutting a corner, driving at high speed on gravel, driving half-on and half-off a bitumen road and with the car appearing as if it was travelling sideways at times.

After crashing into his victims, Buckely slammed into a tree and his car flipped onto its roof.

He was seen trying to push the vehicle back onto its wheels and appeared to be alcohol-affected.

Guy Williams and his partner of nine years Mardi Trease.
(9news)

The County Court of Victoria was told on Tuesday Buckley said to a witness "I don't care" when informed he'd hit two people and a dog.